JP2005070682A - Optical device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device which includes an optical element and a substrate firmly adhered via a metal oxide film, which can be made small in size and easily assembled, and which has favorable insertion loss and an extinction ratio and high reliability, and to provide a method for manufacturing the device. <P>SOLUTION: The optical device having an optical element at least one face of which is adhered to a substrate is characterized in that the optical element is joined to the substrate and a metal oxide film is formed on the joined face of the optical element or the substrate. The method for manufacturing the optical device is also presented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical device having a plurality of optical elements arranged on a substrate, and an optical device in which the optical element and the substrate are bonded via a metal oxide film, and a method for manufacturing the optical device.

  In recent years, with the increase in wavelength of WDM (Wavelength Division Multiplex), the integration of optical communication systems has progressed, and the demand for downsizing of optical devices used therein has also increased.

  In many cases, an optical device is configured by joining an optical element to a fixing member and combining them, but in this method, the fixing member becomes an obstacle and hinders downsizing of the optical device. A method of eliminating the fixing member and bonding the optical elements to each other has been studied.

  For the miniaturization of optical devices, it is effective to join the light-transmitting surfaces of optical elements. The simplest method for joining optical elements is to use an organic adhesive. is there.

  However, the organic adhesive has disadvantages that the outgas has an adverse effect on the laser diode, is weak against high-power laser irradiation and exposure in a high-temperature and high-humidity atmosphere, and lacks device reliability.

  Therefore, a method for bonding optical elements without using an organic adhesive is desired and various studies have been made. Examples of the inorganic bonding material include low melting point glass and solder.

  The conventional optical device 20 shown in FIG. 3 has a configuration in which an optical element 26 is a polarizing glass 22, an analyzer 23, and a Faraday rotator 21 made of bismuth-substituted iron garnet bonded to a substrate 24 with a bonding material 25. ing.

For example, the low-melting glass as the bonding material 25 is mainly composed of a low-melting-point material such as PbO, Bi ₂ O ₃ , or TeO _2. At this time, the antireflective film applied to the optical element 26 and the low melting point glass 25 react with each other, and there is a problem that the antireflection function is impaired. Therefore, the low melting point glass is used for joining the light transmitting surfaces. It is considered difficult.

  On the other hand, when solder is used as the bonding material 25, for example, since there is no translucency, it cannot be placed directly on the translucent surface. Therefore, selective metallization is applied to the outer frame of the translucent surface, and only the metallized portion is soldered. However, a complicated metallization process is required, and it is difficult to avoid a decrease in yield and an increase in cost.

  In view of the above, in recent years, there is a method of directly bonding the optical elements 26 without using any bonding material 25 (see Patent Documents 1 and 2).

  In this method, the surfaces of the optical element 26 are subjected to a hydrophilic treatment, and the hydrophilic surfaces are bonded to each other. In semiconductors, this method is put into practical use in the manufacturing process of SOI (Silicon On Insulator) wafers.

  In FIG. 4A, after forming the metal oxide film 5 on both surfaces of the Faraday rotator 1 and forming the metal oxide film 5 on one surface of the polarizing glasses 2 and 3, polarization is performed as shown in FIG. 1 shows a configuration in which the joining surfaces 6 of the glasses 2 and 3 and the joining surfaces 6 on both surfaces of the Faraday rotator 1 are joined together via a metal oxide film 5 and integrated as an optical element 30.

This direct bonding method greatly depends on the shape and physical properties of the objects to be bonded. For example, with respect to warpage, it is desirable that the radius of curvature is several hundreds m or more, and the arithmetic average surface roughness of the objects to be bonded is Ra. = 0.3 nm or less is said to be desirable, and also greatly affects the difference in coefficient of linear expansion between objects to be joined.
JP-A-7-220923. JP 2000-56265 A.

  However, the joining methods as described in Patent Documents 1 and 2 have the following problems and are difficult to put into practical use.

  For example, an iron-based garnet or the like, which is one of optical elements generally used in an optical device, has a problem that it often involves a large warp because it has a stress distribution in the thickness direction.

  Further, since the polarizing glasses 2 and 3 have a structure in which fine metal particles such as silver and copper are dispersed in the glass, it is difficult to control the arithmetic average surface roughness, and such optical elements 26 are directly bonded to each other. In such a case, there is a problem that peeling at the joint surface 6 is likely to occur and adhesion and durability are low.

  Furthermore, the linear expansion coefficients of these optical elements 26 are often greatly different depending on the material, and there is a large difference in the linear expansion coefficient between objects to be joined. When materials having different linear expansion coefficients are directly bonded, There is a problem that thermal stress is generated between different kinds of materials, and the optical stress is easily generated by concentrating the thermal stress on the joint portion 6, and the optical characteristics such as the extinction ratio are deteriorated.

  In view of the above, the present invention is for solving these problems. In an optical device having a plurality of optical elements arranged on a substrate, the optical element and the substrate are bonded via a metal oxide film. It is characterized by comprising.

Further, the metal oxide film is one or more selected from Al ₂ O ₃ , TiO ₂ , and SiO ₂ .

  Furthermore, the thickness of the metal oxide film is 1 nm or more and 250 nm or less.

  The optical element is a Faraday rotator made of polarizing glass and / or bismuth-substituted iron garnet, and the substrate is made of glass.

  Further, the bonding is performed after forming a metal oxide film on at least one of the bonding surface of the optical element or the substrate in the optical device.

  Further, the method includes a first step of hydrophilizing, cleaning, and drying the metal oxide film, and a second step of heat-treating the optical element and the substrate directly or via water. .

  Further, the heat treatment is performed in a temperature range of 80 ° C. or higher and 300 ° C. or lower.

  As described above, according to the present invention, it is easy to bond an optical element and a substrate and a strong bonding strength is obtained, and there is no outgas generation or deterioration of a bonding surface, and a small and highly reliable optical device is inexpensive. Can be provided.

  Further, since the optical element can be temporarily fixed on the substrate, the optical adjustment can be performed with high accuracy, and the optical device can be easily assembled.

  Further, since it is not necessary to perform high temperature processing as in the case of using solder or the like, there is no fear of warping of the substrate, so that the substrate can be made thin and the length in the optical axis direction can be shortened.

  As a result of various investigations to provide a small and highly reliable optical device at a low cost, the present inventors have determined that the optical element and the substrate are bonded via a metal oxide film. The present inventors have found that the bonding strength between the substrate and the substrate is sufficiently strong and reliable, and that it is advantageous for downsizing, and the present invention has been completed by examining various conditions relating to bonding.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a perspective sectional view showing an optical device completed as a joint between an optical element and a substrate according to the present invention.

  The optical device 10 shown in FIG. 1 is provided with gaps t and t ′ between the optical elements 15 and arranged almost in parallel on the substrate 4, and the optical element 15 and the substrate 4 are oxidized by metal. They are joined via the film 5.

  The optical element 15 includes a Faraday rotator 1 and polarizing glasses 2 and 3, and is bonded after forming the metal oxide film 5 on at least one of the optical element 15 or the bonding surface 6 on the substrate 4.

Preferably, the metal oxide films 5 and 5 ′ are formed of at least one selected from Al ₂ O ₃ , TiO ₂ and SiO _{2 on} at least one of the bonding surfaces 6 of the substrates 4 and 4 ′ opposed to the optical element 15. The metal oxide films 5 and 5 ′ can be laminated in a single layer or multiple layers to increase the bonding strength after the hydrophilic treatment.

  The metal oxide films 5 and 5 ′ formed on the bonding surfaces 6 and 6 ′ of the substrates 4 and 4 ′ can be performed by a normal electron beam evaporation method, and the bonding surfaces 6 and 6 of the optical element 15 or the substrates 4 and 4 ′. Bonding can be performed after the metal oxide films 5 and 5 'are formed on at least one of 6'.

  The metal oxide film layers 5 and 5 ′ are preferably deposited to a thickness of 1 nm or more and 250 nm or less, so that the thickness of the single layer film or the multilayer film is less than 1 nm. Since it becomes large, it becomes difficult to adhere.

  If the Faraday rotator 1 constituting the optical device 10 of the present invention is made of bismuth-substituted iron garnet and the polarizing glasses 2 and 3 and the substrate 4 are made of glass, the adhesion with the metal oxide film 5 is improved, so that the reliability is improved. It will improve and function effectively without affecting the optical properties.

  Next, the manufacturing method of the optical device of this application is demonstrated.

  FIG. 2 is a cross-sectional perspective view showing an embodiment of a manufacturing method until an optical element and a substrate of an optical device of the present invention are bonded through a metal oxide film.

  As shown in FIG. 2 (a), a plurality of optical elements 15 arranged between the two substrates 4, 4 ′ are arranged with gap sizes t, t ′, s, and the optical element 15 and the two substrates 4 are arranged. 4 'has a structure joined through the metal oxide film 5.

  The optical element 15 or the substrates 4 and 4 ′ are bonded to the bonding surfaces 6 and 6 ′ by performing a hydrophilic treatment, a first step of washing and drying, and then directly connecting the optical element 15 and the substrates 4 and 4 ′. Or it joins through water and performs by performing the 2nd process of heat-processing after that.

  Mirror polishing is performed as a pretreatment step, and the target values of the arithmetic average surface roughness (Ra (nm)) and warpage (curvature radius (m)) of the optical element 15 or the joint surfaces 6 and 6 ′ of the substrates 4 and 4 ′ are preferable. For example, the counter-polarizing glasses 2 and 3 are subjected to normal wet mirror polishing so that Ra = 4 nm or less, warpage = 70 nm or more, and the Faraday rotators 4 and 4 ′ are Ra = 3 nm or less and warpage = 40 nm or more. Next, it is more effective to use ordinary wet cleaning together with short-wave ultraviolet treatment (UV treatment) or plasma treatment.

  As a first step, a hydrophilic treatment is performed on the bonding surfaces 6 and 6 ′ of the optical element 15 or the substrates 4 and 4 ′ (for the Faraday rotator 1, metal oxide films 5 and 5 ′ are formed on the bonding surfaces 6 and 6 ′. After that, washing and hydrophilization are performed).

  For hydrophilization treatment, ammonia perwater (a mixture of ammonia water, hydrogen peroxide water, and pure water), nitric acid, hydrochloric acid diluted solution, or these diluted solutions that are generally used in semiconductor SOI wafer processes are peroxidized. An aqueous solution to which hydrogen water is added is effective.

  Then, it is desirable that the hydrophilic treatment liquid is removed by washing with pure water and dried uniformly with a spin dryer or the like.

  After the metal oxide films 5 and 5 ′ are formed on at least one of the bonded surfaces 6 and 6 ′ on the pre-processed optical element 15 or the substrates 4 and 4 ′ obtained in this way, each is brought into close contact, and FIG. As shown in b), the metal oxide films 5 and 5 ′ are formed on at least one of the optical elements 15 or the bonding surfaces 6 and 6 ′ on the substrates 4 and 4 ′, and then bonded.

  In this case, it is particularly preferable to join via water, and it can be joined more easily.

  In the bonding, it is preferable that laser light is transmitted perpendicularly to the optical element 15 and fixed at an angle at which the extinction ratio is maximized.

  Next, as a second step, a necessary and sufficient bonding force is obtained by heat-treating the optical element 15 and the substrates 4 and 4 ′ bonded in the above procedure for several hours, and the temperature is set to about 80 ° C. or more and 300 ° C. or less. Is preferred.

  If the temperature is less than 80 ° C., the effect of increasing the bonding strength cannot be obtained. If the temperature exceeds 300 ° C., the optical element 15 is warped, so that it is difficult to adhere to each other.

  At this time, if the heating rate in the heat treatment process is too high, peeling may occur on the bonding surface 6 during the heating, and it is desirable to set the heating rate to 20 ° C./h or less.

  Further, the atmosphere during the heat treatment does not matter even if it is in the air, but it is more preferable that the atmosphere is a reduced pressure atmosphere or an atmosphere containing hydrogen.

  Through the above steps, the optical element 15 and the substrates 4 and 4 ′ are completely bonded to each other through the metal oxide films 5 and 5 ′, so that the optical device 10 can be completed.

  In this optical device 10, as shown in FIG. 2C, a plurality of optical elements 15 arranged on the substrates 4, 4 ′ are arranged with gap dimensions t, t ′, s, and cut into blocks. A large number can be cut out (dotted lines in the figure indicate cut parts).

  As an example of the optical device of the present invention, the optical device 10 of FIG. 1 was prototyped.

  The plurality of optical elements 15 were bonded to the substrates 4 and 4 ′ with gap sizes t, t ′, and s, respectively.

  The optical element 15 has a polarizing glass 2 and 3 of 15 mm × 2.05 mm × t 0.195 mm and a refractive index of 1.47, a Faraday rotator 1 of 15 mm × 2.05 mm × t 0.420 mm and a refractive index of 2.35, The substrates 4 and 4 ′ are 15 mm × 15 mm × t 0.5 mm and the refractive index is 1.5.

  The gap dimensions t and t 'of each optical element 15 are 0.01 mm, and the gap dimension s is 0.03 mm.

After sufficiently polishing the bonding surfaces 6 and 6 ′ of the optical elements 15, the metal oxide films 5 and 5 ′ are formed on the surfaces of the bonding surfaces 6 and 6 ′ of the optical elements 15 and the substrates 4 and 4 ′ with TiO ₂ , A multilayer laminated film (150 nm) having a refractive index of 1.5 was formed of Al ₂ O ₃ and SiO ₂ .

Further, the laser light passes through a surface other than the joint surface 6 (not shown) of each optical element 15, the transmission surface is perpendicular to the optical axis, and SiO ₂ is deposited on the transmission surface side by 120 nm. .

The refractive index of SiO ₂ was optimized at 1.45, and the antireflection film was optimized at a wavelength of 1.55 μm.

  Next, each optical element 15 was subjected to UV (ultraviolet) treatment with a low-pressure mercury lamp and then subjected to ultrasonic cleaning with pure water.

  Next, as a first step, as a hydrophilization treatment, ammonia water: hydrogen peroxide water: pure water = 1: 1: 4 is immersed in ammonia overwater, and the ammonia overwater is washed away by ultrasonic cleaning with pure water. Drying was performed by steam drying.

  Next, as a second step, the plurality of Faraday rotators 1 are sandwiched between the plurality of polarizing glasses 2 and 3, and the plurality of polarizing glasses 2 and 3 and the plurality of the plurality of polarizing glasses 2 and 6 ′ are interposed via water. The Faraday rotator 1 was disposed on the substrates 4 and 4 ′ with gaps t, t ′ and s.

  At this time, the angle is adjusted so that the polarization directions of the plurality of polarizing glasses 2 and 3 are 45 ° to each other, and the substrates are placed on the substrates 4 and 4 ′, and in a hydrogen atmosphere at 120 ° C. for 12 hours and 0.4 atm. Then, vacuum drying was performed to perform dehydration from the joint surfaces 6 and 6 ′ between the optical elements 15 and the substrates 4 and 4 ′. At this time, the heating rate was 4 ° C./h.

  The optical device 10 is configured according to the above procedure, and a plurality of optical elements 15 and the substrates 4 and 4 ′ are cut into chips of 0.85 × 1 × t1.5 mm by dicing to complete a smaller optical device 10. The length of the optical device 10 in the light transmission direction could be 0.85 mm.

  On the other hand, the optical element 26 used as a comparative example as shown in FIG. 3 is provided with a gold deposition layer on one side of each optical element 26 so that the bonding material 25 can be fixed by soldering. In addition, a stainless steel (SUS304) flat plate 1.05 mm × 3.2 mm × t 0.5 mm was used for the substrate 24, and the surface was plated with gold so that soldering became possible.

  A gold-tin high temperature solder foil (melting point: 280 ° C.) was placed on the substrate 24 where each member was fixed, and a polarizing glass 22, an analyzer 23, and a Faraday rotator 21 were placed thereon.

  At this time, the gap dimensions of the polarizing glass 22, the analyzer 23, and the Faraday rotator 21 are t2 and t3 arranged at intervals of 0.05 mm, heated to 350 ° C. by high-frequency heating with the substrate 24, and soldered as a bonding material 25. The optical device 20 was completed.

  The length of the optical device 20 in the light transmission direction was 1.05 mm, which is the minimum dimension t2 provided to prevent the solder from filling the gap between the optical elements 26 with surface tension. , T3.

  Eleven samples of the optical devices 10 and 20 of the examples of the present invention and the comparative example were produced, and optical characteristics (forward insertion loss and reverse insertion loss) were measured.

Measurement conditions of the optical characteristics was carried out optical wavelength lambda _c 1550 nm, the optical output intensity of the laser at 0dBm or 1 mW.

  For the measurement system, measurement was performed using a Hewlett Packard HP8153A optical multimeter as a power meter, a HP81553SM series as a fixed laser light source module, and a HP81531A series as an optical power sensor module.

Table 1 shows the optical property evaluation results of the optical devices of the examples and comparative examples of the present invention under the above measurement conditions.

  Thereby, the average of 11 forward insertion losses of the Example of this invention was 0.10 dB, and the average of backward insertion loss was 45 dB.

  Moreover, the average of 11 forward insertion losses of the comparative example was 0.13 dB, and the average of backward insertion loss was 39 dB.

  It was confirmed that the optical characteristics were sufficiently better than those of the comparative examples, and those values were also stable.

  As is clear from the above results, the value of the reverse insertion loss in which the angular deviation between the polarizing glass and the Faraday rotator is particularly significant is considerably worse than the results of the examples, and the values of the individual optical devices are also The variation was large.

  This is thought to be because the angle adjustment between the polarizing glass and the Faraday rotator shifted at the time of soldering.

  Also, in the optical device using solder, a large thermal stress is generated, so that the isolation characteristic is remarkably deteriorated.

  Moreover, in the optical device according to the present invention, it is understood that the optical characteristics are good and stable because the accuracy of the angle adjustment between the polarizing glass and the Faraday rotator is ensured.

  In addition, since the polarizing glass and the Faraday rotator are adhered and bonded to the substrate, it is possible to reduce the size particularly in the light transmission direction.

  As described above, the long-term stability of the optical device in which the optical element and the substrate are bonded via the metal oxide film is realized.

It is a section perspective view showing one embodiment of the optical device of the present invention. (a)-(d) is a cross-sectional perspective view which shows the preparation methods of the optical device of this invention. It is a cross-sectional perspective view which shows the conventional optical device. (a), (b) is sectional drawing which shows the conventional optical device.

Explanation of symbols

1, 21 Faraday rotator 2, 3, 22 Polarizing glass 4, 4 ′ glass substrate 5, 5 ′ metal oxide film 6, 6 ′ bonding surface 10, 20, 30 Optical device 15, 26 Optical element 23 Analyzer 24 Substrate 25 Bonding material t, t ′, s, t2, t3

Claims (7)

An optical device having a plurality of optical elements arranged on a substrate, wherein the optical element and the substrate are bonded via a metal oxide film. The optical device according to claim 1, wherein the metal oxide film is one or more selected from Al ₂ O ₃ , TiO ₂ , and SiO ₂ . The optical device according to claim 1, wherein a thickness of the metal oxide film is 1 nm or more and 250 nm or less. The optical device according to any one of claims 1 to 3, wherein the optical element is a Faraday rotator made of polarizing glass and / or bismuth-substituted iron garnet, and the substrate is made of glass. 5. A method for manufacturing an optical device, comprising: forming a metal oxide film on at least one of an optical element and a bonding surface of a substrate in the optical device according to claim 1; 6. The method according to claim 5, comprising a first step of hydrophilizing, cleaning and drying the metal oxide film, and a second step of bonding the optical element and the substrate directly or through water to perform heat treatment. Optical device manufacturing method. The method of manufacturing an optical device according to claim 6, wherein the heat treatment is performed in a temperature range of 80 ° C. or more and 300 ° C. or less.

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